Question 1

A patient develops a bloodstream infection after a catheter is inserted. Laboratory analysis reveals the presence of a dense microbial community attached to the catheter surface. Which of the following best explains why this infection is particularly difficult to treat with antibiotics?

Accepted Answer

Biofilms provide a protective environment that increases resistance to antibiotics.

Question 2

Which of the following best describes the role of superoxide dismutase in bacterial cells?

Accepted Answer

It removes superoxide radicals, a toxic form of oxygen.

Question 3

A microbiologist is culturing a bacterium that grows best at 37°C and is commonly found in human infections. Which group does this organism most likely belong to?

Accepted Answer

Mesophiles

Question 4

Which of the following equations correctly represents the number of cells $$N$$ after $$n$$ generations, starting from a single cell, during the log phase of binary fission?

Accepted Answer

$$N = 2^n$$

Question 5

A bacterium is isolated from a salt lake and requires a minimum of 15% NaCl for growth. Which term best describes this organism?

Accepted Answer

Extreme halophile

Question 6

Which of the following best explains why molds and yeasts are able to spoil acidic foods such as fruit preserves more readily than most bacteria?

Accepted Answer

They grow best at lower pH values than most bacteria.

Question 7

A culture medium contains only glucose, ammonium phosphate, magnesium sulfate, sodium chloride, potassium phosphate, and water. Which type of medium is this?

Accepted Answer

Chemically defined medium

Question 8

During which phase of the bacterial growth curve does the rate of cell death equal the rate of new cell formation?

Accepted Answer

Stationary phase

Question 9

A bacterium is able to grow in the presence or absence of oxygen, but grows better when oxygen is present. Which term best describes this organism?

Accepted Answer

Facultative anaerobe

Question 10

Which of the following is a correct statement about agar as used in microbiological media?

Accepted Answer

Agar solidifies at approximately 40-45°C.

Question 11

A researcher is studying a bacterium that can use light for energy and organic compounds as a carbon source. Which nutritional type does this organism represent?

Accepted Answer

Photoheterotroph

Question 12

Which of the following trace elements is most likely required as a cofactor for enzymes involved in electron transport?

Accepted Answer

Iron

Question 13

A bacterial culture is preserved by rapidly freezing it at -80°C. Which preservation method is being used?

Accepted Answer

Deep-freezing

Question 14

Which of the following best describes the function of buffers in culture media?

Accepted Answer

They prevent drastic changes in pH.

Question 15

A bacterium is found to require oxygen but is killed by atmospheric concentrations of oxygen. Which term best describes this organism?

Accepted Answer

Microaerophile

Question 16

Which of the following best explains why obligate anaerobes are often harmed by oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 17

A bacterial population increases from 1,000 to 8,000 cells in 3 hours. Assuming exponential growth, what is the generation time? Use the formula $$n = \frac{\log N_t - \log N_0$}{\log 2}$$, where $$n is $$the number of generations, $$N_t is $$the final cell number, and $$N_0 is $$the initial cell number. Then, generation time $$g = \frac{t}{n}.$$

Accepted Answer

30 minutes

Question 18

Which of the following statements about biofilms is correct?

Accepted Answer

Biofilms are associated with dental caries and heart valve infections.

Question 19

Which of the following best describes the role of nitrogen in microbial growth?

Accepted Answer

It is required for the synthesis of DNA, RNA, and proteins.

Question 20

A bacterium is able to grow in a medium with or without salt, but grows best at 10% NaCl. Which term best describes this organism?

Accepted Answer

Facultative halophile

Microbial Growth: Physical and Chemical Requirements, Growth Phases, and Culture Methods

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